Vacuum tube for heavy currents



May 1, 1934. H, M. FREEMAN VACUUM TUBE FOR HEAVY CURRENTS Original Filed March 29. 1924 INVENTOR ffuber M. Freeman ATTORNEY Patented May 1, 1934 UNITED STATES ISS'ZZ PATE VACUUM TUBE FOR HEAVY CURRENTS Application March 29, 1924, Serial No. 702,716 Renewed September 22, 1933 7 Claims.

This invention relates to vacuum tube devices of the type used for controlling space currents.

It is an object of this invention to produce a device of the class described which can convey a greater space current for a given size of device than has been possible with devices of this class heretofore.

It is a further object of this invention to provide a device in which the heat developed at the anode may be removed by means of a stream of cooling fluid.

It is a further object of this invention to provide a device of the class described in which the cathode may be heated by a coil out of electrical contact therewith, the heating being accomplished by thermal conduction.

It is a further object of this invention to provide a heating device for the cathode which can be readily renewed when necessary.

It is a further object of this invention to provide means for minimizing the escape of heat, from the heating coil, into the surrounding atmosphere.

It is a further object of this invention to so arrange the several parts of the device that a compact apparatus is produced without reducing the size of the electrode surfaces.

Other objects of my invention and details of the construction will be better understood from the following description and the accompanying drawings in which Figure 1 is a central vertical sectional viewof one form of the device,

Fig. 2 is a similar view of a different modication.

' The device includes a glass envelopeorcontainer 1, which, preferably, is highly evacuated,

but the device may still be operated with improved results when there is gas remaining with- 0 in the envelope.

The anode consists of a coil 2 of metal. Copper, silver, or other good thermal conductor, may be used. Each end of this coil passes through the glass envelope, as indicated at 3 and 4. A

suitable seal between the metal tubing and the glass is made at each of these ends, in order that the vacuum within the envelope may be preserved.

The anode is surrounded by any convenient form of grid. Preferably, the grid is e henx 5, which is supported by a standard 6, welded to each turn of the helix. The standard extends through the envelope at '7 and serves as a conductor by means of which potentials may be .55 applied to the grid.

(Cl. Z50-27.5)

The cathode consists of a cylindrical plate 8, of a metal that is adapted to withstand high temperatures, such as tungsten. er platinum. 'The inner surface of the plate 8 is preferably coated with a material that will emit electrons abun- 50 dantly when the plate is hot. A mixture of the oxides of barium and strontium serves this purpose well, but other coatings of a high emission power may be used. The cylindrical plate may be supported by a standard 10, which also serves as a lead or conductor, or it maybe supported in other Ways as described below, and the lead 10 will then serve only as a conductor.

Conoentric with the cylindrical cathode, is a heating coil 1l. In the ferm shown in Figure 1, 70 this coil is outside of the container 1.

Escape of heat from the coil 11 into the outer `atmosphere is prevented or minimized by a covering 14e of heat-insulating material. Preferably, this covering and the coil 1l are made to con- 75 stitute a single unit which can be slipped onto the tube from the small end and will be stopped' in the proper position by the enlargement `at the upper end of the tube.

When current is passed through the coil l1 to 80 heat it, heat will flow through the glass wall 13 and raise the temperature of the metallic cylinder 8. The emission of electrons from the coated inner surface of this cylinder will thus be increased. The heat is constrained to pass through the glass wall instead of into the surrounding atmosphere by the heat insulation 14.

The cathode 8, preferably fits closely against the inner face of this cylinder. Any of the usual methods for obtainingv a close union between the metallic cylinder 8 and the glass cylinder 13 may be followed. For example, the inner surface of the glass may be silvered and a platinum `nlm electro-chemically deposited on the silver. A tungsten cathode may be sealed directly to the inner surface of the glass in the same way that tungsten wire is sealed into the glass when making the usual connections for vacuum devices. The barium and strontium salts, or other coating material, may be applied to the cathode after it is in place.

In the form shown in Fig. 2, the envelope comprises a re-entrant portion l5, having cylindrical walls, preferably concentric with the outer cylindrical walls. This gives the container the form of a double-walled cylinder having a hollow top but with a single wall at the bottom. The reentrant portion bounds a recess,r within which the coil 1l is located. The convex surface of the reentrant portion, Which is the surface inside of the container, joins the cylindrical lcathode 8. The union between the two may be formed in any of the ways described with Fig. 1.

Preferably, the coil 1l is of a diameter to fit closely the inner, that is to say, the concave face of the re-entrant portion VY15. To prevent the heat, developed in the coil 11, from passing into the outer atmosphere, the mouth of the reentrant portion of the envelope is closed by a glass wall 16. The ends of the coil pass through this closure in order that current may be supplied thereto and are sealed therein to prevent leakage. The closure 16 is preferably supplied with a thinner portion 17 near its junction with the wall of the container. i

When the coil 11 is burned out, it may be replaced by breaking the closure 16 at the thin part. A new ccil, withY a new closure sealed therctdinay then be put in place. A joint between the new closure and the container may be formed, Vby the use of smeltz glass, or by any similar glass-blowers expedient, The space containing the coil 11 is tlen evacuated and sealed as indicated by the sealing tip 18.

By exhausting the space containing the coil 11, the difference in pressure between the interior of the container and this space, may be made very small so that, Yeven if the cylindrical part of the re-entrant portion 15 be heated beyond the point at which glass begins toy weaken, no damage results.

In the operation of the device, current, which may be either direct or alternating, is supplied to the coil 11 to heat it. The coil heats the cathode and so produces electron emission. A difference of pctential between the cathode and the anode may be supplied by means of the lead 10 and an external part of the coiled tube, which causes a space current from the anode 2 to the cathode 8. The bombardment of the anode by the electrons constituting this space current heats the anode, but heat is rapidly removed therefrom by the stream of water or other cooling fluid flowing through the coiled anode. Y

If the container 1 is highly exhausted, the space current is made up wholly of the electron stream, but if gas be present, ions also will take part in the spacecurrent A much larger current may be carried in the latter case and Ya much greater quantity of heat will be liberated at the anode, but, because of the provision for cooling the anode with a stream oi fluid, the device will transmitn large amounts ofY power without the necessity of building it in prohibitive sizes.

It will be evident to those skilled in the art that many variations of structure may be made Without departing from the spirit of this invention. The fact that I have illustrated but three chamber for maintaining it at an elevated temforms of the device is not to be construed as a limitation, no limitations except those necessiltated by the prior art or expressed by the claims being intended. i i

I claim as my invention:

1. In a thermionic device, a cylindrical cathode a heating coil concentric therewith, an evacuated container enclosing said cathode and separating said heating coil therefrom and means for constraining the heat to flow from said coil through the wall of said container to said cathode.

2. In a thermionic device, anevacuated container having a re-entrant portion of insulating material, a cathode within the container and in contact with the re-entrant part of Ythe wall ranged between the cylindrical walls of said envelope and aheating coil inside of the inner wall of said envelope. Y

4. In an electronic device, an envelope comprising a double-walled cylinder having a hollow end, a coiled tubular anode, a helical grid and a cylindrical cathode, concentrically arranged between the cylindrical walls of said envelope, a heating coil inside of the inner wall of said envelope and a single-wall closure for the hollow end of thecontainer.

5. In an electronic device, an envelope comprising a double-walled insulating cylinder having a hollow end, a coiled tubular anode, a helical grid and a cylindrical cathode, concentrically ar- Y ranged between the cylindrical walls of said en- =1 velope and a heating coil inside ofthe inner wall Y of said envelope, the cathode andY heating device being in close proximity to opposite faces of the,Y inner wall of the container.

6. An electrical discharge device comprising an anode and a cathode consisting of a chamber of vitrecus material coated on its interior walls Ywith material which emits electrons freely when heated and means on the exterior wall of said perature. e Y l 7. In a space-current device, an envelope comprising an insulating cylindrical wall, the

thermionically-emissive cathode on one side of ilo said wall and a heating device for said cathode on the other side thereof and in contact with said wall.

HUBERT M. FREEMAN. 

